1. Field of the Invention
The present invention relates to systems for detecting and protecting against undesired side loads on rotatable equipment, such as may be applied to the booms of mobile cranes. In particular, the present invention relates to systems using pressure sensors to detect excessive side load and shut off appropriate equipment functions in response thereto.
2. Description of the Prior Art
It is frequently desirable to detect and protect against excessive torques on rotatable equipment, such as caused by undesirable side loads applied to the boom ends of mobile crane-like devices commonly known as xe2x80x9cdigger derricksxe2x80x9d. Such rotatable devices are designed to accommodate limited and predictable controlled loads. Unpredictable side loads on the boom can occur during various types of operations, including winching a load from the side or screwing an anchor at an angle into the ground with a digger. Excessive side loads can cause substantial damage to the equipment""s structure and operating mechanisms.
Several systems exist for protecting against excessive side loads. These systems typically attempt to sense undesired load levels and respond with appropriate action when pre-established limits are exceeded. For example, one existing system uses relief valves that open when pressure increases in a hydraulic motor due to back driving under excessive side load torque. Pressure relief allows the booms to slip toward the load, thereby reducing the side load torque. However, boom slippage does not work well in all situations (i.e., working on excessive slopes).
Another existing system translates thrust loads on an internal worm drive shaft into hydraulic pressure and then disables load-related functions using a preset hydraulic pressure switch. This latter system, however, does not compensate for different mechanical efficiencies between the clockwise and counterclockwise directions of rotation because the system utilizes a single common pressure setting. Furthermore, an undesirably large amount of hysteresis can occur between the actuation and reset values.
The side load detection and protection system of the present invention includes enabling technology that overcomes the disadvantages of existing systems to make the monitoring and mitigation of torques or side loads applied to rotatable equipment more reliable, and operation of the equipment more predictable. The preferred system determines side load as a function of the difference in media pressure between two ports of a pneumatic/hydraulic rotation motor. When the side load reaches or exceeds a pre-established limiting value, the system shuts off equipment functions likely to be causing or contributing to the side load. The system includes a visual display to communicate the amount of actual side load and to communicate a warning when the side load limit has been reached or exceeded.
The system is able to differentiate between loads applied to the rotation mechanism through operation of the pneumatic/hydraulic rotation mechanism and external side loads applied to the boom creating an excessive torque. Furthermore, in order to account for different efficiencies, the system can be adjusted for different threshold settings in the clockwise and counterclockwise directions.